This invention relates generally to steam turbine engines, and more particularly, to bolt assemblies used with steam turbine engines.
At least some known steam turbine engines include an upper half casing and a lower half casing wherein the upper half casing includes a horizontal joint flange feature and the lower half casing includes a horizontal joint flange feature. The upper half horizontal joint casing flange and the lower half horizontal joint casing flange are coupled together with a number of bolt and nut assemblies. At least one known bolt assembly, sometimes referred to as a “through” bolt assembly, includes a single bolt, suitably threaded on both ends, and a pair of nuts that are used to couple the pair of flanges together. For example, a single threaded bolt may be inserted through an opening defined within each flange. Moreover, a first nut may be threadably coupled to a first end of the bolt such that the first nut is substantially flush with a surface of the first horizontal joint flange, and a second nut may be threadably coupled to a second end of the bolt such that the second nut is substantially flush with a surface of the second horizontal joint flange. This at least one known bolt assembly is often referred to as a “through” bolt assembly. During assembly of at least one known “through” bolt assembly, when the bolt is inserted through a flange opening, the bolt will fall out of the opening until at least one nut is coupled to the bolt to retain the bolt within the flange. Coupling a nut to the bolt can present difficulty due to space constraints around each flange and due to the difficulty of simultaneously tightening both ends of the bolt assembly.
At least one known bolt assembly, sometimes referred to as a “tapped” bolt assembly, is used when structural sub-assemblies of a steam turbine engine are completely contained within the body of the engine making access to the sub-assembly difficult. At least one known “tapped” bolt assembly includes a threaded hole integral to the lower half horizontal joint flanges. The threaded hole eliminates the need for a second nut coupled to the second horizontal joint flange. Threading the hole integral to a horizontal joint flange can present difficulty due to space constraints. Moreover, during assembly and use of the “tapped” bolt assembly, the threads integral to the horizontal joint flange may be easily worn and/or stripped. When the threads of the hole integral to the horizontal joint flange are worn and/or stripped, the threads are difficult to repair and/or replace.